Pour soy sauce, water, and vinegar into a large, non-metallic bowl. Whisk in brown sugar, white sugar, pepper, sesame oil, garlic, and onion until the sugars have dissolved. Submerge the ribs in this marinade, and cover with plastic wrap. Refrigerate 7 to 12 hours; the longer, the better.

Preheat an outdoor grill for medium-high heat. Remove ribs from the marinade, shake off excess, and discard the marinade. Cook on preheated grill until the meat is no longer pink, 5 to 7 minutes per side.